The objectives of this proposal are to characterize biochemically the estrogen-elevated polypeptide growth factors which our initial studies suggest are involved in rat pituitary tumor cell growth in vivo and in vitro. The rat pituitary tumor cell line to be used in these studies was established by this laboratory as a sub-clone of the original GH3 rat pituitary tumor cell population. The unique property of this line (designated GH3/C14) is that after more than four years in culture inoculation of the long term grown cells into host rats shows the same estrogen-responsive tumor formation as shown for the original clone. The GH3/C14 cells demonstrate both 4s cytoplasmic and 5s nuclear estrogen specific receptors, and translocate cytoplasmic labeled estradiol to the nucleus in a temperature process comparable to normal rat target tissues. Nevertheless, when tested in culture there is no growth promotion effect seen with estrogens under a wide variety of test conditions. We have attempted to resolve this apparent contradiction by approaching the problem of estrogen-promoted tumor cell growth from a new direction. We concluded that it may be possible for estrogens to induce production and secretion of specific growth factors which would enter the blood and promote growth of distant hormone-responsive type tumor cells. Initial evidence for a mediated mechanism of estrogen mitogenicity was obtained by identifying estrogen-inducible rat pituitary growth factor (PGF) activities in extracts of rat uterus and rat kidney, showing that the estrogen-inducible uterine activity was a polypeptide material with relative specificity for the type of cells which form estrogen-responsive tumors, and identification of PGF in uterine luminal fluid accumulated in response to estrogens. In this proposal, our purpose is to continue studies to establish conclusively the in vivo involvement in the mechanism estrogens yields uterus, kidney yields specific polypeptide growth factors which yields pituitary tumor cell growth.